Polymers having reactive terminal silyl groups or compositions comprising such polymers can be hydrolyzed and condensed in the presence of water and organometal catalysts. Suitable known catalysts for curable compositions include organometallic compounds employing metals such as Sn, Ti, Zn or Ca. Organotin compounds such as, for example, dibutyltin dilaurate (DBTDL) are widely used as condensation cure catalysts to accelerate the moisture assisted curing of a number of different polyorganosiloxanes and non-silicone polymers having reactive terminal silyl groups such as room temperature vulcanizing (RTV) formulations including RTV-1 and RTV-2 formulations. Environmental regulatory agencies and directives, however, have increased or are expected to increase restrictions on the use of organotin compounds in formulated products. For example, while formulations with greater than 0.5 wt. % dibutyltin presently require labeling as toxic with reproductive 1B classification, dibutyltin-containing formulations are proposed to be completely phased out in consumer applications during next 4-6 years.
Alternative organotin compounds such as dioctyltin compounds and dimethyltin compounds can only be considered as a short-term remedial plan, as these organotin compounds may also be regulated in the future. It would be beneficial to identify non-Sn metal catalysts that accelerate the condensation curing of moisture curable silicones and non-silicones. Desirably, substitutes for organotin catalysts should exhibit properties similar to organotin compounds in terms of curing, storage, and appearance. Non-tin catalysts would also desirably initiate the condensation reaction of the selected polymers and complete this reaction upon the surface and may be in the bulk in a desired time schedule. There are therefore many proposals for the replacement of organometallic tin compounds by other organometallic compounds. These other metals have specific advantages and disadvantages in view of replacing tin compounds perfectly. Therefore, there is still a need to overcome some of the weaknesses of possible metal compounds as suitable catalyst for condensation cure reaction and behavior of uncured and cured compositions in particular to maintain the ability to adhere onto the surface of several substrates.
The use of iron (III) and bismuth (III) complexes as catalysts in condensation curable silicone compositions has been described. For example, U.S. Pat. Nos. 7,550,547 and 7,115,695 describe the use of iron carboxylate as a catalyst for cross-linking silyl-capped organic polymers, with and without carboxylic acids, respectively. U.S. Pub. No. 2011/0021684 and 2011/0040034 describes the synthesis and use of iron complexes that contain both diketonate or enolate anions and monovalent anions as catalysts in RTV-organosiloxane compositions. U.S. Pat. Nos. 4,404,348 and 3,936,578 claim the use of iron acetylacetonates as catalyst in solventless organosiloxane coating/impregnating compositions. U.S. Pat. No. 5,932,650 describes the use of iron carboxylate to improve high temperature adhesion of RTV-1 silicone composition which comprises organometallic tin as condensation cure catalyst. U.S. Pat. No. 5,985,991 broadly claims the use of among others, e.g., iron acetylacetonate in a generic list of metal acetylacetonates consisting of Cu, Cr, Al, Zn, Ti and Zr to improve the oil resistance of RTV silicone composition which comprises metal salt of carboxylic acid as a condensation cure catalyst. U.S. Pat. No. 5,945,466 broadly claims among others, e.g. organic metal compounds containing Fe in a generic list of organic metal compounds containing Sn, Ti, Zr, Pd, Zn, Co, Mn and Al as metallic element, as curing catalyst for room temperature curable organopolysiloxane composition which contains organosilane or its hydrolyzed product among other components.
U.S. Publication Nos. 2003/0069379 claims the use of trivalent bismuth carboxylates as curing catalyst in room temperature curing organopolysiloxane composition. U.S. Publication No. 2011/0009558 and 2011/0021684 claims the use of Bi(monoallyl ethylene glycolate)3 and Bi(1,1,1,5,5,5-hexafluoropentanedionate)3 as catalysts, respectively, in curable organopolysiloxane compositions. U.S. Pat. No. 7,365,145 generically claims, among others, organo iron and organo bismuth compounds in a generic list of organic dibutyltin, zirconium complex, aluminum chelate, titanium chelate, organic zinc, organic cobalt, and organic nickel as catalysts in moisture curable silylated polymer composition. U.S. Pat. No. 5,194,489 claims the use of bismuth carboxylate as hardening catalyst for crosslinkable cyclopentenyl containing diorganopolysiloxane composition which also comprises an inorganic filler. U.S. Publication No. 2009/0156737 claims among others Lewis acid compounds of bismuth in a generic list of Lewis acid compounds of Ti, Zr, Hf, Zn, B, Al as catalysts in polymer blends comprising alkoxy silane terminated polymers and fillers. Similar generic descriptions on the use of bismuth carboxylate in curable silicone composition are made in U.S. Publication no. 2009/306307. U.S. Pat. No. 7,504,468 claims the use of mixture organometallic compounds which include among others bismuth compounds as catalyst in single component silicone compositions. U.S. Publication no. 2005/0137322 claims the use of a bismuth catalyst in a second component along with a polyol in two component coating composition comprised of a compound containing trialkoxysilyl and isocyanate functional groups as a first component.
U.S. Pat. No. 4,293,597 includes Fe and Bi salts of mono- or di-carboxylic acids in a generic list of metal salts including Pb, Sn, Zr, Sb, Cd, Ba, Ca, and Ti as catalysts in curable silicone rubber compositions that also contains nitrogen-functional silanes. U.S. Pat. No. 4,461,867 includes Fe and Bi metal esters in a generic list of metal esters also including Sn, Pb, Zr, Sb, Cd, Ba, Ca, Ti, Mn, Zn, Cr, Co, Ni, Al, Ga and Ge as a catalyst in moisture curable RTV-1 silicone compositions. U.S. Pub. No. 2011/0098420 includes, among others, Fe and Bi compounds in a generic list also including compounds of Pt, Pd, Pb, Sn, Zn, Ti and Zr, as dehydrogenative condensation reaction catalyst for a curable polysiloxane composition comprising of siloxanes with 2 or more hydrosilyl groups and siloxanes with 2 or more silanol groups. U.S. Pat. No. 7,527,838 claims, among others, Fe and Bi based catalysts in a generic list which includes other metal catalysts based on Sn, Ti, Zr, Pb, Co, Sb, Mn and Zn, in curable diorganopolysiloxane compositions used for making insulated glass units. U.S. Publication number 2002/0156210 claims the use of catalyst composition that is the combination of or the reaction products of ingredients comprising iron containing compounds that include, among others, iron carboxylates and iron acetylacetonates, silyl phosphates and organoaluminium compounds in the process of forming conjugated diene polymers.
Despite these general teachings that group iron or bismuth complexes together with other metal catalysts, there has not been provided any teachings or catalyst compositions that differentiate the catalytic activity exhibited by different iron or bismuth complexes. Further, there has not been a replacement catalyst for organo-tin compounds that maintains its ability to cure after storage over months in a sealed cartridge, when exposed to humidity or ambient air. It is always a specific requirement for moisture curable compositions to achieve the shortest possible curing times, showing a tack-free surface as well as a curing through the complete bulk in thick section for “One-Part” and “Two-Part” Room-Temperature Vulcanizing (RTV) compositions and provide a reasonable adhesion after cure onto a variety of substrates.